Surface treatment process of CMP Polishing pad

ABSTRACT

A surface treatment process of a CMP (chemical mechanical polishing) polishing pad includes steps of rough-machining, fine-machining and finish-machining a substrate in sequence with an abrasive belt with a particle size of 120-mesh, an abrasive belt with a particle size of 240-mesh and an abrasive belt with a particle size of 400-mesh, respectively till a target thickness of the substrate is obtained. In each processing stage, the surface of the substrate is sanded through effectively adjusting the height of the corresponding abrasive belt so as to effectively control a surface roughness of the substrate. Moreover, through the surface treatment process provided by the present invention, the initial surface roughness is consistent with the surface roughness in the usage process of the substrate, so as to solve the problem that the initial grinding rate is unstable, thereby significantly improving the stability of the substrate in the CMP process.

CROSS REFERENCE OF RELATED APPLICATION

The present invention claims priority under 35 U.S.C. 119(a-d) to CN 201810971728.7, filed Aug. 24, 2018.

BACKGROUND OF THE PRESENT INVENTION Field of Invention

The present invention relates to the processing and manufacturing field of CMP (chemical mechanical polishing) polishing pads, and more particularly to a surface treatment process of a CMP polishing pad.

Description of Related Arts

Chemical mechanical polishing (CMP) is a micro-nano processing technology that combines mechanical grinding with chemical oxidation to remove the surface material of machined workpieces. The surface of the machined workpieces is ultra-flat and ultra-smooth through the CMP process, so that the CMP process is mainly used in the field of IC and MEMS manufacturing. The polishing procedure combines chemical corrosion with mechanical friction, the machined workpiece is fixed to a face-down grinding head and fixed to a rotary machine station. The surface of the rotary machine station is covered with a polishing pad, and the abrasive slurry with small abrasive particles flows onto the surface of the rotary machine station. The surface material of the machined workpiece is invaded by the grinding particles, and is gradually ground, and then washed away by the abrasive slurry. Due to the combined action of the rotational friction of two rails and the abrasive slurry, the surface of the workpiece is polished. The polishing pad plays a very important role in the CMP process. Therefore, people have carried out a lot of researches on the characteristics of the polishing pad and its action on the CMP process. Polyurethane polishing pads are widely used in the field of chemical mechanical polishing due to their excellent properties.

The main parameter for evaluating the polishing effect is the grinding rate. The main factors affecting mechanical polishing are the surface roughness of the polishing pad, the concentration and flow rate of slurry, and the rotation speed of the rotary machine station. In the polishing process, in addition to the contact with the wafer surface, the polishing pad needs a diamond grinding disc to continuously polish the surface of the polishing pad at a certain speed, so as to maintain a certain surface roughness of the polishing pad while scraping off excess slurry.

At present, the mainstream production process of the polyurethane polishing pad comprises shaping the raw material by a casting process, slicing the shaped raw material, and then performing the subsequent processes. Due to the strict requirements of the thickness of the product after being sliced, the current research on the slicing process mainly focuses on the thickness control, and the surface roughness of the product after being sliced is not monitored and controlled. Due to different initial surface roughness of the polishing pad, the contact areas of the product to be polished are different, resulting in different initial grinding rates, so that the initial grinding rate of most polishing pads is unstable during use.

SUMMARY OF THE PRESENT INVENTION

Aiming at deficiencies mentioned above, an object of the present invention is to provide a surface treatment process of a CMP (chemical mechanical polishing) polishing pad, so as to solve the problem that the initial grinding rate is unstable in the chemical mechanical grinding process, thus improving the stability of the polishing pad in the whole polishing process.

A surface treatment process of a CMP (chemical mechanical polishing) polishing pad comprises steps of:

(S1) determining a final target thickness of a substrate to be D mm;

(S2) rough-machining the substrate, which comprises selecting a first abrasive belt with a particle size of 120-mesh, placing the substrate in a sanding machine, sanding the substrate in an alternating manner of a front surface and a reverse surface of the substrate, adjusting a height of the first abrasive belt for several times while changing the front surface and the reverse surface of the substrate till the thickness of the substrate is D+(0.08-0.10) mm;

(S3) fine-machining the substrate, which comprises selecting a second abrasive belt with a particle size of 240-mesh, placing the substrate below the second abrasive belt, sanding the substrate in the alternating manner of the front surface and the reverse surface of the substrate, adjusting a height of the second abrasive belt for several times while changing the front surface and the reverse surface of the substrate till the thickness of the substrate is D+(0.01-0.02) mm; and

(S4) finish-machining the substrate, which comprises selecting a third abrasive belt with a particle size of 400-mesh, placing the substrate below the third abrasive belt, sanding the substrate in the alternating manner of the front surface and the reverse surface of the substrate, adjusting a height of the third abrasive belt for several times while changing the front surface and the reverse surface of the substrate till the thickness of the substrate reaches the final target thickness of D mm.

It should be noted that, the alternating manner of the front surface and the reverse surface of the substrate means that the front surface of the substrate is firstly sanded, and then the height of the corresponding abrasive belt is adjusted, and then the reverse surface of the substrate is sanded. Here, the substrate is sanded in the alternating manner of the front surface and the reverse surface of the substrate for many times, preferably, for twice. In addition, the height of the corresponding abrasive belt is adjusted through adjusting a gap width between an upper roller and a lower roller of a sanding machine; the corresponding abrasive belt is installed on the upper roller and the lower roller; the substrate is placed between the upper roller and the lower roller for being sanded.

Preferably, in the step of (S2), an adjusted height of the first abrasive belt every time is not more than 0.09 mm.

Preferably, in the step of (S3), an adjusted height of the second abrasive belt every time is not more than 0.04 mm.

Preferably, in the step of (S4), an adjusted height of the third abrasive belt every time is not more than 0.02 mm.

It should be noted that the height of every abrasive belt is measured and adjusted through an operational panel of the sanding machine.

Compared with the prior art, the present invention has some beneficial effects as follows. The surface of the substrate is sanded by sanding belts with different meshes to control the surface roughness of the substrate, so that the initial surface roughness of the substrate is consistent with the surface roughness of the substrate during use, thereby solving the problem of unstable initial grinding rate. The surface treatment process of the substrate provided by the present invention significantly improves the stability of the polishing process of the substrate. In addition, the present invention has characteristics of simple operation, easy monitoring of performance indexes after being processed, and strong process implementation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a contrast result of a surface roughness of a substrate before and after being sanded by an abrasive belt with a particle size of 120-mesh provided by the present invention.

FIG. 2 shows a contrast result of a surface roughness of a substrate before and after being sanded by an abrasive belt with a particle size of 240-mesh provided by the present invention.

FIG. 3 shows a contrast result of a surface roughness of a substrate before and after being sanded by an abrasive belt with a particle size of 400-mesh provided by the present invention.

FIG. 4 shows a contrast result of a grinding rate of unsanded products and sanded substrates.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

To further understand the present invention, the method and effect provided by the present invention are described with reference to embodiments in detail as follows.

A sanding machine is available through market purchase. In the present invention, a model of the sanding machine is Buffing machine TS100D.

A method for detecting a thickness of a substrate comprises steps of: measuring four different positions of the substrate by a vernier caliper, respectively recording four thickness values of the four different positions, and finally taking an average value of the four thickness values as a final thickness value.

First Embodiment

In the roughing process, a first abrasive belt with a particle size of 120-mesh and a substrate with a thickness of 2.65 mm are used, the substrate is placed in a sanding machine, a height of the first abrasive belt is adjusted to 2.56 mm, a front side of the substrate is sanded for a period of time and then the height of the first abrasive belt is adjusted to 2.47 mm, and then a reverse side of the substrate is sanded, and the thickness of the substrate is 2.47 mm measured by a vernier caliper.

In the fine process, a second abrasive belt with a particle size of 240-mesh is used, the above substrate is placed in the sanding machine, a height of the second abrasive belt is adjusted to 2.43 mm, the front side of the substrate is sanded for a period of time and then the height of the second abrasive belt is adjusted to 2.39 mm, and then the reverse side of the substrate is sanded, and the thickness of the substrate is 2.39 mm measured by the vernier caliper.

In the finishing process, a third abrasive belt with a particle size of 400-mesh is used, the above substrate is placed in the sanding machine, a height of the third abrasive belt is adjusted to 2.37 mm, the front side of the substrate is sanded for a period of time and then the height of the third abrasive belt is adjusted to 2.35 mm, and then the reverse side of the substrate is sanded, and then the substrate is sanded in accordance with above mentioned procedures in following stages, wherein an adjusted height of the corresponding abrasive belt every time is not more than 0.02 mm till the thickness of the substrate is 2.30 mm.

Second Embodiment

In the roughing process, a first abrasive belt with a particle size of 120-mesh and a substrate with a thickness of 2.65 mm are used, the substrate is placed in a sanding machine, a height of the first abrasive belt is adjusted to 2.56 mm, a front side of the substrate is sanded for a period of time and then the height of the first abrasive belt is adjusted to 2.47 mm, and then a reverse side of the substrate is sanded, and then the height of the first abrasive belt is adjusted to 2.39 mm, and then the front side of the substrate is sanded, and the thickness of the substrate is 2.39 mm measured by a vernier caliper.

In the fine process, a second abrasive belt with a particle size of 240-mesh is used, the above substrate is placed in a sanding machine, a height of the second abrasive belt is adjusted to 2.36 mm, the front side of the substrate is sanded for a period of time and then the height of the second abrasive belt is adjusted to 2.33 mm, and then the reverse side of the substrate is sanded, and the thickness of the substrate is 2.33 mm measured by the vernier caliper.

In the finishing process, a third abrasive belt with a particle size of 400-mesh is used, the above substrate is placed in the sanding machine, a height of the third abrasive belt is adjusted to 2.32 mm, the front side of the substrate is sanded for a period of time and then the height of the abrasive belt is adjusted to 2.31 mm, and then the reverse side of the substrate is sanded for a period of time, and then the height of the third abrasive belt is adjusted to 2.30 mm, and then the front side of the substrate is sanded again till the thickness of the substrate is 2.30 mm.

In order to verify the effect of the surface treatment process provided by the present invention, relevant parameters of some of the products of the above two embodiments are measured.

(1) A method for measuring a roughness comprises steps of:

measuring four different positions of a product by a roughness instrument, respectively recording four roughness magnitudes of the four different positions, and finally taking an average value of the four roughness magnitudes as a final roughness magnitude. Products according to the first embodiment of the present invention are selected randomly and divided into four groups, the roughness of the substrate at each stage of the sanding treatment are respectively measured to obtain specific results of the roughness, which are shown in FIGS. 1 to 3.

It can be seen from FIGS. 1 to 3, after the front surface of the substrate is processed by the abrasive belts with 100-mesh, 240-mesh and 400-mesh, respectively, the roughness of the substrate is kept within a range of 2000-3000 Ra, thereby effectively controlling the roughness of the product.

(2) Stability test of the initial grinding rate:

Experimental procedures are as follows. The product in the first embodiment and the unsanded product are respectively made into a polishing pad in the same manner, and then the polishing pad is mounted on the polishing machine for actual machine testing. The polishing machine is a fully automatic machine. During the polishing process, the grinding rate is monitored in different time periods, and the result is directly fed back to a computer, which is shown in FIG. 4.

It can be seen from FIG. 4 that a polishing pad made from a substrate that has not been sanded has a large difference between an initial grinding rate and a later grinding rate during the grinding process, so that the stability of the polishing pad is poor during the overall grinding process. However, a polishing pad made from a substrate that has been sanded has an initial grinding rate basically consistent with a later grinding rate during the grinding process, and has high stability. In summary, the stability of the product during the polishing process can be improved by controlling the stability of the surface roughness of the product, especially the stability of the initial grinding rate.

The above is only the preferred embodiment of the present invention, and is not intended to limit the protective scope of the present invention. The protective scope of the present invention is defined by the appended claims. Equivalent structural changes made by using the contents of the specification of the present invention should be included in the protective scope of the present invention. 

What is claimed is:
 1. A surface treatment process of a CMP (chemical mechanical polishing) polishing pad, comprising steps of: (S1) determining a final target thickness of a substrate to be D mm; (S2) rough-machining the substrate, which comprises selecting a first abrasive belt with a particle size of 120-mesh, placing the substrate in a sanding machine, sanding the substrate in an alternating manner of a front surface and a reverse surface of the substrate, adjusting a height of the first abrasive belt for several times while changing the front surface and the reverse surface of the substrate till the thickness of the substrate is D+(0.08-0.10) mm; (S3) fine-machining the substrate, which comprises selecting a second abrasive belt with a particle size of 240-mesh, placing the substrate below the second abrasive belt, sanding the substrate in the alternating manner of the front surface and the reverse surface of the substrate, adjusting a height of the second abrasive belt for several times while changing the front surface and the reverse surface of the substrate till the thickness of the substrate is D+(0.01-0.02) mm; and (S4) finish-machining the substrate, which comprises selecting a third abrasive belt with a particle size of 400-mesh, placing the substrate below the third abrasive belt, sanding the substrate in the alternating manner of the front surface and the reverse surface of the substrate, adjusting a height of the third abrasive belt for several times while changing the front surface and the reverse surface of the substrate till the thickness of the substrate reaches the final target thickness of D mm.
 2. The surface treatment process, as recited in claim 1, wherein in the step of (S2), an adjusted height of the first abrasive belt every time is not more than 0.09 mm.
 3. The surface treatment process, as recited in claim 1, wherein in the step of (S3), an adjusted height of the second abrasive belt every time is not more than 0.04 mm.
 4. The surface treatment process, as recited in claim 1, wherein in the step of (S4), an adjusted height of the third abrasive belt every time is not more than 0.02 mm. 